I can only get this far on this problem:
You have to set the problem to 0
so, x^2 + 12x -8x + 4 + 3=0
x^2 + 4x + 7 = 0
I think there's is more to it though.
(x+ __) (x + ___)=0
then you have to set them to 0. (sove for x)
x+___ = 0
x+___=0
then, you check it
Hope it helped though.